Towards a kilometre-scale Earth System Model to better predict extreme weather events: insights from the Destination Earth initiative's case studies.

This presentation will showcase research conducted at the European Centre for Medium-Range Weather Forecasts (ECMWF) as part of the Destination Earth initiative of the European Commission. This initiative aims to develop a continuous global component of Earth's Digital Twin of Weather-induced and Geophysical Extremes (Extremes DT) to be able to forecast and monitor extreme weather events with unprecedented precision worldwide within a five-day range.

We will discuss various model experiments used to evaluate how horizontal resolution, ocean-atmosphere coupling, and different forecast initializations affect the prediction of some extreme weather events (i.e. medicanes, winter European storms, or extreme alpine precipitation, among others). In the current Extremes DT, ECMWF's Integrated Forecasting System cycle 48r1 is being used with a Tco2559 grid (approximately 4.5 km in horizontal resolution). We will compare the performance of these simulations with the current ECMWF's operational deterministic 9km forecasts and even higher resolution forecasts and we will validate the simulations with high-density observations and model analyses.

This research shows the significant benefits of higher resolution in predicting near-surface fields in specific case studies, especially large precipitation amounts in regions with complex orography, and the potential for more accurate medicane forecasts (both location and intensity). However, variables such as maximum wind gusts require additional development, such as enhancing data assimilation and reviewing parametrization formulations, and evaluation using high-density observations. For these goals to be achieved, we conclude that other aspects of global models need to be improved alongside increased resolution. Ultimately, our work provides valuable insights into evaluating and improving Earth System models on a kilometre-scale.